Piston for internal combustion engines



NOV. 10, 1931. J w 5 PISTON FOR INTERNAL COMBUSTION ENGINES Filed Dec.10. 1928 V r I A.

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Patented Nov. 10, 1931 JOHANN WEISS, OF VIENNA, AUSTRIA PISTON FORINTERNAL COMBUSTION ENGINES Application filed December 10, 1928, SerialNo. 324,859, and in Austria April 12, 1928.

My invention relates to improvements in pistons consisting of a lightmetal or of a1- loys of such metals and intended for use in internalcombustion engines.

5 As the materials of pistons of this kind have a greater coeflicient ofexpansion than the material, generally cast iron, of which the cylinderis made, provision has been made to allow the piston to freely expandwithin the cylinder or the piston has been constructed in such a mannerthat when cold it snugly fits into-the cylinder walls but is allowed toundergo deformations under the action of heat so as to prevent grippingor freezing on 1 the cylinder walls.

My present invention resides on the consideration that no precautions orprovisions with respect to the dimensions or to the exe cution of thepiston in view of heat expansion would be necessary if the heat enteringfrom the combustion chamber through the head of the piston into thepiston itself could be successfully carried away so rapidly that theheat in the material of the piston does not manifest itself by expansionphenomena. This of course cannot be attained in an abso lutely perfectmanner but provision can be made to prevent accumulation or banking upof heat and consequently also to prevent considerable expansions in thematerial of the piston. These provisions may consist, when making use ofthe usual alloys of light metals for the manufacture of-the piston, insupplying the inner surface ofsuch a piston with a covering or lining ofa metal, for example copper, or of an alloy which has a greater power togive off heat than the material itself of which the piston is made Theheat of the piston material isthen given off more rapidly to the mediumfilling the interior of the piston, i. e. air or oil, than in the caseof the absence of the covering or lining, the com sequence being amaterial decrease of the heat ex ansion of the piston.

urthermore constructing the piston so as to have onthe innerside of itshead extensions or projections which in consequence of their dimensionsor shape have a low resistonce against heat conduction, it is possibleto attain a deviation of the heat flow away from the skirt of the pistontowards the interior of the piston, so that the skirt is heated only toa relatively small degree and consequently does not expand at all,practically speaking, because the main part of the heat is conducted toa place in the interior of the piston, where this heat is rapidly givenoff to the medium in the interior of the piston by means of the coveringor lining of excellent heat conductivity.

In practice it has been found possible, by

the use of this invention, to form a piston with a skirt which may bemade to fit the cylinder snugly when cold and yet no gripping orfreezing because of heat expansion will occur during operation and thisiis accom plished without providing slits or the like in the skirt torender it yielding.

One form of a piston according tomy invention is illustrated in theaccompanying drawings, which shows in Figs. 1 and 2 axial sections ofthe piston taken on two vertical plans perpendicular to each other,whereas Fig. 3 is a view from below.

1n the represented example the said covering or-lining of part of theinner wall of the piston with a metal of higher heat conductivity iscarried out by embedding a hollow ring of copper a directly at the innerside of the piston. The hollow ring of copper a is, as may be seen inthe drawing embedded between the head I) of the piston and the bearingbosses c of the gudgeon of the connecting rod, this ring being put intothe casting mould like a core, in addition to the core which correspondsto the hollow part of the piston; to this end a unitary core issufficient. The hollow ring is entirely covered by the molten lightmetal poured into the mould and the core for the hollow part of thepiston may be so shaped as to form between the hollow copper ring a andthe cavity of the piston next the bearing bosses a relative- 1y thickannular portions 65 (Fig. 1) consisting of light metal whereas, betweenthe two bearing bossesc, the innerwall a, and the adjoining wall a, ofthe hollow copper'ring a (which latter wall is directed towards the openside of the piston) define thecavity of the piston. When the piston istaken out of the mould, its wall a will be provided with perforations e(Fig. 3) or cut out totally bea tween the two bearing bosses, so thatthe ton or the oil in this cavity can freely pass into cavity of thecopper ring a and since this latter receives the heat from the head ofthe piston in the shortest way and gives it off very easily, the heatpassing through it is rapidly transmitted to the medium circulating inthe interior of the piston.

Besides, the piston may be so shaped that the thickness of its wall onthe outer side of the copper ring a, particularly owing to the presenceof the grooves g for the reception of the piston rings is considerablyless than in the center of the head 6 of the piston and it is also lessthan the thickness of the wall between the copper ring a and the head 6.The resistance against heat conduction therefore increases graduallytowards the sliding surface of the piston so that the heat is more orless accumulated in the center of the piston head and is transmittedmore easil to the copper ring than to the skirt 5. T e high coefficientof heat conductivity of the copper ring enables such a rapid giving offof the heat so that this heat is prevented from being conducted into Ithe skirt '5 of the piston to a considerable de- The deviation of thestream of heat away from part) of the piston wall and away from theskirt 2' is favored by the relatively thick webs d (Fig. 1) throughwhich part of the heat of the head I) of the piston is conducted to thebearing bosses 0 and therefrom to the gudgeon of the connectingrod'respectively to the rod itself so that also in this manner heat iscarried awayand prevented to flow towards the skirt 2' to a materialdegree.

Experiments have shown that a piston in conformity with the describedexample of an embodiment of my invention may be made to snugly fit intothe cylinder when .cold and that it does not expand in the normaloperation as to cause an undue wear of the cylinder by abrasion or afreezing or gripping.

It is to be understood that the covering or lining of the inner wall .ofthe piston with a better heat conducting material may be carried outalso in other ways, e. g. by means of any metallizing process. Of coursethe inner wall in its totality may be provided with a covering or liningof the said kind.

to increase the power of giving off heat. The property of copper or ofanother material to possess a lower coefficient of expansion thanaluminum or alloys thereof may be made use of. In unitingla layer ofcopper and a layer of aluminum so intimately as to form a compoundmaterial, this latter has then .a lower coefiicient of expansion thanaluminum or alloys thereof. Therefore when uniting the lining of theinner wall of the piston with the material of the piston by means of anintermediate layer which improves the firm adherence or by usingmechanical means such as double tail feather and groove connection, orthe like in such an intimate manner that relative movements of bothlayers are impossible, a double effect is secured, viz. (1) a rapidgiving 01f of heat and (2) a decrease of the coeflicient of expansion.This enables and facilitates giving to the piston a snug sliding fitbearing on the inner wall of the cylinder when cold.

Where in the specification and claims the expression light metal isused, this expression means aluminum and aluminum alloys, such as alloysof aluminum with magnesium, copper and other metals. The range of metalsis, however, not to be restricted just to these metals. The piston isessentially of a light metal. This expression is used in the artgenerally to mean a metal lighter than irons and steels and this use ofthe expression light metal is accepted by workers in this art. The metalwhich is adapted to give off heat rapidly is, therefore, a metal havinga higher heat conductivity than the light metal.

What I claim is: I

1. In combination with a piston consisting of light metal, a hollow ringof a material adapted to give off heat more rapidly than said lightmetal, said ring being embedded at the inner side of the piston head inthe material of the piston, the said hollow ring and the piston materialsurrounding it being provided on the side towards the interior of thepiston with perforations to permit a circulation through the cavity ofthe ring of the medium which fills the interior of the piston.

2. In combination with a piston consisting of light metal, a hollow ringof a material adapted to give off heat more rapidly than said lightmetal, said ring being embedded at the inner side of the piston head inthe material of the piston, the said hollow ring and the piston materialsurrounding it being provided on the side towards the interior of thepiston with perforations to permit a circulation through the cavity ofthe ring of the medium which fills the interior of the piston, the ringand the surrounding piston material being located in the space betweenthe piston body and the bearing bosses for the gudgeons of theconnecting rod.

In testimony whereof I affix my signature.

J OHANN WEISS.

